Disclosed herein is an ink composition comprising a humectant blend comprising a first humectant and a second humectant; wherein the first humectant has a freezing point; wherein the second humectant suppresses the freezing point of the first humectant such as to impart to the ink composition the characteristic of being able to be stored at a desired temperature without solidifying; water; an optional co-solvent; an optional colorant; and a sulfonated polyester.
Further disclosed is a process of digital offset printing, the process comprising applying an ink composition onto a re-imageable imaging member surface at an ink take up temperature, the re-imageable imaging member having dampening fluid disposed thereon; forming an ink image; transferring the ink image from the re-imageable surface of the imaging member to a printable substrate at an ink transfer temperature; wherein the ink composition comprises a humectant blend comprising a first humectant and a second humectant; wherein the first humectant has a freezing point; wherein the second humectant suppresses the freezing point of the first humectant such as to impart to the ink composition the characteristic of being able to be stored at a desired temperature without solidifying; water; an optional co-solvent; an optional colorant; and a sulfonated polyester.
Digital architectures for lithographic inks is an important emerging technology. There is a need for expanded ink compositions suitable for this technology. Food grade printing inks for digital lithographic ink printing are desired. There is a need for non-UV (ultra violet) curable compositions for digital offset ink, such as for water-based ink formulations.
Typical lithographic and offset printing techniques utilize plates that are permanently patterned, and are, therefore, useful only when printing a large number of copies of the same image, such as magazines, newspapers, and the like. Variable data digital lithography or digital offset lithographic printing has been developed as a system that uses a non-patterned re-imageable surface, which is initially uniformly coated with a dampening fluid layer. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source) to form pockets. A temporary pattern in the dampening fluid is thereby formed over the non-patterned re-imageable surface. Ink applied thereover is retained in the pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate, such as paper, plastic or metal and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new uniform layer of dampening fluid applied to the re-imageable surface, and the process repeated.
Digital offset printing systems use offset-type inks that are specifically designed and optimized to be compatible with the materials the ink is in contact with, including the re-imageable surface and the dampening solution as well as with the various subsystems used during the printing process to enable high quality digital printing at high speed.
For example, an inker subsystem may be used to apply a uniform layer of ink over the layer of dampening fluid. The inker subsystem may use an anilox roller to meter the ink onto one or more ink forming rollers that are in contact with the re-imageable surface. The ink used with this subsystem should have a viscosity that is not so high that anilox-take up and delivery to the re-imageable surface is difficult. However, too low of a viscosity, tack and/or poor cohesion may result in the ink crawling out of the ink loader, resulting in unwanted spills, loss of ink and potential contamination of the printer. Accordingly, digital offset inks should have a certain range of viscosity, tack and tack stability to afford sufficient and predictable ink cohesion to enable good transfer properties in and among the various subsystems.
An exemplary digital offset printing architecture is shown in FIG. 1. As seen in FIG. 1, an exemplary system 100 may include an imaging member 110. The imaging member 110 in the embodiment shown in FIG. 1 is a drum, but this exemplary depiction should not be interpreted so as to exclude embodiments wherein the imaging member 110 includes a plate or a belt, or another now known or later developed configuration. The re-imageable surface 110(a) may be formed of materials including, for example, a class of materials commonly referred to as silicones, including flurosilicone, among others. The re-imageable surface may be formed of a relatively thin layer over a mounting layer, a thickness of the relatively thin layer being selected to balance printing or marking performance, durability and manufacturability.
U.S. patent application Ser. No. 13/095,714 (“714 Application”), entitled “Variable Data Lithography System,” filed on Apr. 27, 2011, by Timothy Stowe et al., which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety, depicts details of the imaging member 110 including the imaging member 110 being comprised of a re-imageable surface layer 110(a) formed over a structural mounting layer that may be, for example, a cylindrical core, or one or more structural layers over a cylindrical core.
The imaging member 110 is used to apply an ink image to an image receiving media substrate 114 at a transfer nip 112. The transfer nip 112 is formed by an impression roller 118, as part of an image transfer mechanism 160, exerting pressure in the direction of the imaging member 110. Image receiving medium substrate 114 includes, but is not limited to, any particular composition or form such as, for example, paper, plastic, folded paperboard, Kraft paper, clear substrates, metallic substrates or labels. The exemplary system 100 may be used for producing images on a wide variety of image receiving media substrates. The 714 Application also explains the wide latitude of marking (printing) materials that may be used.
The exemplary system 100 includes a dampening fluid system 120 generally comprising a series of rollers, which may be considered as dampening rollers or a dampening unit, for uniformly wetting the re-imageable surface of the imaging member 110 with dampening fluid. A purpose of the dampening fluid system 120 is to deliver a layer of dampening fluid, generally having a uniform and controlled thickness, to the re-imageable surface of the imaging member 110. It is known that a dampening fluid such as fountain solution may comprise mainly water optionally with small amounts of isopropyl alcohol or ethanol added to reduce surface tension as well as to lower evaporation energy necessary to support subsequent laser patterning, as will be described in greater detail below. Small amounts of certain surfactants may be added to the fountain solution as well. Alternatively, other suitable dampening fluids may be used to enhance the performance of ink based digital lithography systems. Exemplary dampening fluids include water, Novec 7600 (1,1,1,2,3,3-Hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)pentane.), and D4 (octamethylcyclotetrasiloxane). Other suitable dampening fluids are disclosed, by way of example, in co-pending U.S. Pat. No. 9,592,699, the disclosure of which is hereby incorporated herein by reference in its entirety.
Once the dampening fluid is metered onto the re-imageable surface of the imaging member 110, a thickness of the dampening fluid may be measured using a sensor (not shown) that may provide feedback to control the metering of the dampening fluid onto the re-imageable surface of the imaging member 110 by the dampening fluid system 120.
After a precise and uniform amount of dampening fluid is provided by the dampening fluid system 120 on the re-imageable surface of the imaging member 110, an optical patterning subsystem 130 may be used to selectively form a latent image in the uniform dampening fluid layer by image-wise patterning the dampening fluid layer using, for example, laser energy. Typically, the dampening fluid will not absorb the optical energy (IR or visible) efficiently. The re-imageable surface of the imaging member 110 should ideally absorb most of the laser energy (visible or invisible such as IR) emitted from the optical patterning subsystem 130 close to the surface to minimize energy wasted in heating the dampening fluid and to minimize lateral spreading of heat in order to maintain a high spatial resolution capability. Alternatively, an appropriate radiation sensitive component may be added to the dampening fluid to aid in the absorption of the incident radiant laser energy. While the optical patterning subsystem 130 is described above as being a laser emitter, it should be understood that a variety of different systems may be used to deliver the optical energy to pattern the dampening fluid.
The mechanics at work in the patterning process undertaken by the optical patterning subsystem 130 of the exemplary system 100 are described in detail with reference to FIG. 5 in the 714 Application. Briefly, the application of optical patterning energy from the optical patterning subsystem 130 results in selective removal of portions of the layer of dampening fluid.
Following patterning of the dampening fluid layer by the optical patterning subsystem 130, the patterned layer over the re-imageable surface of the imaging member 110 is presented to an inker subsystem 140. The inker subsystem 140 is used to apply a uniform layer of ink over the layer of dampening fluid and the re-imageable surface layer of the imaging member 110. The inker subsystem 140 may use an anilox roller to meter an offset lithographic ink, such as the ink compositions of the present disclosure, onto one or more ink forming rollers that are in contact with the re-imageable surface layer of the imaging member 110. Separately, the inker subsystem 140 may include other traditional elements such as a series of metering rollers to provide a precise feed rate of ink to the re-imageable surface. The inker subsystem 140 may deposit the ink to the pockets representing the imaged portions of the re-imageable surface, while ink on the unformatted portions of the dampening fluid will not adhere to those portions.
The cohesiveness and viscosity of the ink residing in the re-imageable layer of the imaging member 110 may be modified by a number of mechanisms. One such mechanism may involve the use of a rheology (complex viscoelastic modulus) control subsystem 150 which may optionally comprise a heating system. The rheology control system 150 may form a partial crosslinking layer of the ink on the re-imageable surface to, for example, increase ink cohesive strength relative to the re-imageable surface layer. Curing mechanisms may include optical or photo curing, heat curing, drying, or various forms of chemical curing. Cooling may be used to modify rheology as well via multiple physical cooling mechanisms, as well as via chemical cooling. For non-curable ink, the rheology control system may comprise a heater or other rheology control device, or may be omitted.
The ink is then transferred from the re-imageable surface of the imaging member 110 to a substrate of image receiving medium 114 using a transfer subsystem 160. The transfer occurs as the substrate 114 is passed through a nip 112 between the imaging member 110 and an impression roller 118 such that the ink within the voids of the re-imageable surface of the imaging member 110 is brought into physical contact with the substrate 114. With the adhesion of the ink, such as the ink of the present disclosure, having been modified by the rheology control system 150, modified adhesion of the ink causes the ink to adhere to the substrate 114 and to separate from the re-imageable surface of the imaging member 110. Careful control of the temperature and pressure conditions at the transfer nip 112 may allow transfer efficiencies for the ink, such as the ink of the present disclosure, from the re-imageable surface of the imaging member 110 to the substrate 114 to exceed 95%. While it is possible that some dampening fluid may also wet substrate 114, the volume of such a dampening fluid may be minimal, and may rapidly evaporate or be absorbed by the substrate 114.
In certain offset lithographic systems, it should be recognized that an offset roller, not shown in FIG. 1, may first receive the ink image pattern and then transfer the ink image pattern to a substrate according to a known indirect transfer method.
Following the transfer of the majority of the ink to the substrate 114, any residual ink and/or residual dampening fluid may be removed from the re-imageable surface of the imaging member 110, typically without scraping or wearing that surface. An air knife may be employed to remove residual dampening fluid. It is anticipated, however, that some amount of ink residue may remain. Removal of such remaining ink residue may be accomplished through use of some form of cleaning subsystem 170. The 714 Application describes details of such a cleaning subsystem 170 including at least a first cleaning member such as a sticky or tacky member in physical contact with the re-imageable surface of the imaging member 110, the sticky or tacky member removing residual ink and any remaining small amounts of surfactant compounds from the dampening fluid of the re-imageable surface of the imaging member 110. The sticky or tacky member may then be brought into contact with a smooth roller to which residual ink may be transferred from the sticky or tacky member, the ink being subsequently stripped from the smooth roller by, for example, a doctor blade.
The 714 Application details other mechanisms by which cleaning of the re-imageable surface of the imaging member 110 may be facilitated. Regardless of the cleaning mechanism, however, cleaning of the residual ink and dampening fluid from the re-imageable surface of the imaging member 110 may be used to prevent ghosting in the system. Once cleaned, the re-imageable surface of the imaging member 110 is again presented to the dampening fluid system 120 by which a fresh layer of dampening fluid is supplied to the re-imageable surface of the imaging member 110, and the process is repeated.
Digital offset printing systems use offset-type inks that are specifically designed and optimized to be compatible with the materials the ink is in contact with, including the re-imageable surface and the dampening solution as well as with the various subsystems used during the printing process to enable high quality digital printing at high speed.
For example, an inker subsystem may be used to apply a uniform layer of ink over the layer of dampening fluid. The inker subsystem may use an anilox roller to meter the ink onto one or more ink forming rollers that are in contact with the re-imageable surface. The ink used with this subsystem should have a viscosity that is not so high that anilox-take up and delivery to the re-imageable surface is difficult. However, too low of a viscosity, tack and/or poor cohesion may result in the ink crawling out of the ink loader, resulting in unwanted spills, loss of ink and potential contamination of the printer. Accordingly, digital offset inks should have a certain range of viscosity, tack and tack stability to afford sufficient and predictable ink cohesion to enable good transfer properties in and among the various subsystems.
U.S. patent application Ser. No. 15/262,809, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof an ink composition useful for digital offset printing applications includes a colorant and a high viscosity thickening agent. The ink is formulated to incorporate a gellant into the ink set to help meet the requirement of two different viscosity or temperature pairs at two different stages of the ink delivery process. In lithography imaging a bulk ink is first transferred onto an anilox roll and then onto the imaging cylinder blanket. The first transfer from bulk ink to anilox roll requires the ink to have a low viscosity while the transfer from roll to imaging blanket requires a high viscosity. The addition of the gellant will increase the viscosity difference within the allowable temperature range thus increasing process latitude and robustness.
U.S. patent application Ser. No. 15/262,871, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof an ink composition useful for digital offset printing applications includes a colorant and a high viscosity thickening agent. The ink is formulated to incorporate polyester viscosity modifier to help meet the requirement of two different viscosity or temperature pairs at two different stages of the process. In digital offset printing a bulk ink is first transferred onto an anilox roll, and then from the anilox roll onto the imaging cylinder blanket. During the bulk ink to anilox roll the disclosed ink has a low viscosity while the transfer from roll to imaging blanket the ink has a higher viscosity. The addition of the polyester viscosity modifier increases the viscosity difference within the allowable temperature range, thus, increasing process latitude and robustness.
Digital offset printing architectures require offset type inks that are specifically designed and optimized to be compatible with the different subsystems, including ink delivery system and imaging system, that enable high quality printing at high speed with no residual.
Digital offset printing inks differ from conventional inks because they must meet demanding rheological requirements imposed by the lithographic printing process while being compatible with system component materials and meeting the functional requirements of sub-system components, including wetting and transfer. Print process studies have demonstrated that higher viscosity is preferred for ink transfer to digital lithography imaging blanket from the inker unit via a roll and yet even higher viscosity is needed to improve transfer to a print substrate. Therefore, there remains a need for digital advanced lithography imaging inks to have increased viscosity latitude to enable excellent ink transfer from the ink loader system at both about 60° C. and excellent ink delivery from the anilox roller to the fluorosilicone blanket at temperatures as low as about 20° C.
Previous ink compositions for digital offset inks required curable monomers, were low viscosity, or required significant water evaporation.
U.S. Pat. No. 9,644,105, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof an ink composition or ink concentrate for variable data lithographic printing or ink jet printing includes a nanoparticle polymer or blend of nanoparticle polymers, wherein the polymer or polymers of the blend are water dispersible at temperatures below 100 degrees Celsius; and solids content is in an amount of greater than 25 percent by total weight.
While currently available ink compositions may be suitable for their intended purposes, a need remains for improved digital offset printing inks, in particular, digital offset printing inks that are free of curable monomers, for example ultra-violet (UV) curable monomers, where the risk of migration of UV ink components limits the use of such UV inks for applications such as food packaging. Further a need remains for digital offset printing inks exhibiting desirable inking from the anilox delivery system, wetting to the blanket substrate, and blanket transfer to the print substrate (for example paper or film). Further, a need remains for digital offset printing inks having a wider temperature latitude for storage stability at various temperatures while preserving the desired storage qualities such as inert, modest vapour pressure, water miscibility, and desired inking and release properties.
The appropriate components and process aspects of the each of the foregoing U. S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.